Bridge system for connecting networks

Abstract

A large number of local area networks are each connected to a backbone network through a network interface module (NIM). The NIM transmits messages from one local area network to another local area network across the backbone network by enveloping the local area network message inside the data field of a backbone network message. Each of the NIM constructs a table of addresses. The backbone network messages are each addressed to the particular destination NIM. The destination NIM receives the backbone network message and de-envelopes it for transmission over its own local area network.

I claim: 
     
       1. A network interface module (NIM) for connecting a local area network to a backbone network comprising: a first interface means connected to a local area network for transmitting and receiving local area network messages to and from said local area network;   a second interface means connected to a backbone network for transmitting and receiving backbone network messages to and from said backbone network;   a memory means connected to said first and second interface means for storing a bridge identification address of a particular NIM, a table of addresses, and for temporarily storing said local area network and backbone network messages; and   a logic means connected to the first and second interface means and the memory means for storing a local area network source address in said local area network message in said table of addresses in association with said bridge identification address of said particular NIM, comparing a destination address in said local area network message with said table of addresses, and if the destination address is associated with the bridge identification address of said particular NIM, then ignoring said local area network message, and if the destination address is associated with a bridge identification address of a NIM other than said particular NIM, then enveloping said local area network message in a backbone network message having a header specifically addressed to said other NIM, and if the destination address is not associated with any of the addreses in said address table then enveloping said local area network message in a backbone netowrk message addressed to be multicast to all other NIMs on said backbone network, the logic means also being for storing local area network source address information in said backbone message in said table of addresses in association with a bridge identification address in said backbone message, and de-enveloping said backbone network message for transmission to said local area network.   
     
     
       2. The device of claim 1 wherein, the logic means envelopes a local area network message into a backbone network message by puttinq the local area network message into the data field of a backbone message, adding a destination address frame comprised of either a bridge identification address or a multicast address, and adding a source address frame comprised of said bridge identification address of this particular NIM.   
     
     
       3. The device of claim 2 wherein, the logic means further envelopes a local area network message and a backbone network message by calculating a backbone frame check sequence and adding it after said data field of said backbone message.   
     
     
       4. The device of claim 3 wherein, the logic means de-envelopes a backbone message by using the backbone frame check sequence to verify the accuracy of said backbone message and if it is a valid message, then the logic means takes the entire data field of the backbone message and passes it to the first interface means for transmission to the local area network.   
     
     
       5. The device of claim 1 wherein, the second interface means is an interface co-processor.   
     
     
       6. The device of claim 1 wherein, the backbone network is a token bus network.   
     
     
       7. A method for connecting a local area network to a backbone network comprising the steps of: connecting a first interface means to a local area network, for transmitting and receiving local area network messages to and from said local area network;   connecting a second interface means to a backbone network, for transmitting and receiving backbone network messages to and from said backbone network;   connecting a memory means to said first and second interface means, said memory means containing a bridge identification address of a first bridge and a table of addresses;   connecting a logic means to said first and second interface means and said memory means, wherein said logic means, said first and second interface means and said memory means comprise a first bridge;   receiving a local area network message in said first interface means and temporarily storing said local area network message in said memory means;   using the logic means to store information from a local area network source address in said local area network message in said table of addresses in association with said bridge identification address of said first bridge;   using said logic means to compare a destination address in said local area network message with said table of addresses, and if the destination address is associated with the bridge identification of said first bridge which is stored in said memory means, then ignoring said local area network message, and if the destination address is associated with a bridge identification address of a second bridge, then enveloping said local area network message in a backbone network message addressed to said second bridge, and if the destination address is not associated with any of the bridge addresses in said address table, then enveloping said local area network message in a backbone network message addressed to be multicast to all other bridges on said backbone network;   receiving and evaluating a backbone network message at said second interface means and temporarily storing said backbone network message in said memory means if said backbone network message is valid;   using said logic means for storing local area network source address information in said backbone message in said table of addresses in association with a birdge identification address in said backbone message; and   using said logic means for de-enveloping a valid backbone message for transmission to said local area network.   
     
     
       8. A method for connecting a local area network to a backbone network comprising the steps of: connecting a local area network to a backbone network by means of a first bridge having an address table and first bridge address;   receiving a local area network message from said local area network at said first bridge and comparing a node address in a node destination frame of said local area network message with said address table, and if said node address is associated with said first bridge address then ignoring said local area network message, and if said node address is associated with a second bridge address then enveloping said local area network message in a data frame of a backbone network message having a bridge destination frame containing said second bridge address for transmission to said backbone network, and if said node address is not associated with any bridge addresses, then enveloping said local area network message in a data frame of a backbone network message having a bridge destination frame containing a multicast address for transmission to said backbone network; and   receiving a backbone network message from said backbone network at said first bridge, and if a bridge address in a bridge destination address frame of said backbone network message is equal to either a multicast address or said first bridge address, then de-enveloping a local area network message contained in a data frame of said backbone message and transmitting said local area network message to said local area network.   
     
     
       9. The method of claim 8 wherein, said enveloping further comprises adding a bridge source frame containing said first bridge address.   
     
     
       10. The method of claim 9 wherein, said table of addresses in said first bridge is constructed by receiving local area network messages from said local area network and associating a node address contained in a node source frame of said local area network message with said first bridge address, and receiving backbone network messages at said first bridge from said backbone network and associating a node address contained in a node source frame of said backbone network message with a bridge address contained in a bridge source frame in said backbone network message.   
     
     
       11. A bridge system for connecting networks, comprising a plurality of local area networks, each local area network comprising a plurality of nodes and each node having a unique node address, each network connected to a bridge and each bridge having a unique bridge address, each bridge connected to a backbone network, and wherein each bridge comprises: mesans for transmitting and receiving a local area network message to and from a first local area network;   means for transmitting and receiving a backbone network message to and from said backbone network;   a storage means for storing a table of addresses associating each node address with its respective bridge address;   means for comparing a node address in a destination node frame in a local area network message received from said first local area network with said table of addresses, and if said node address is associated with a bridge address, then enveloping said local area network message received from said first local area network in a backbone network message data frame, said backbone network message having a bridge destination frame containing said bridge address, and transmitting said backbone message to said backbone network.   
     
     
       12. A bridge system for connecting networks, comprising a plurality of local area network, each local are a network comprising a plurality of nodes and each node having a unique node address, each network connected to a bridge and each bridge having a unique bridge address, each bridge connected to a backbone network, and wherein each bridge comprises: means for transmitting and receiving a local area network message to and from a first local area network;   means for transmitting and receiving a backbone network message to and from said backbone network;   a storage means for storing a table of addresses associating each node address with its respective bridge address; and   means for comparing a node address in a destination node frame in a local area network message received from said first local area network with said table of addresses, and if said node address is associated with a bridge address of this particular bridge, then ignoring local area network message, and if said node address is associated with a bridge address other than a bridge address for this particular bridge, then enveloping said local area network message received from said first local area network in a backbone message data frame, said backbone message having a bridge destination frame containing said bridge address, and transmitting said backbone message to said backbone network.   
     
     
       13. A bridge system for connecting networks, comprising a plurality of local area networks, each local area network comprising a plurality of nodes and each node having a unique node address, each network connected to a bridge and each bridge having a unique bridge address, each bridge connected to a backbone network, and wherein each bridge comprises: means for transmitting and receiving a local area network message to and from a first local area network;   means for transmitting and receiving a backbone network message to and from said backbone network;   a storage means for storing a table of addresses associating each node address with its respective bridge address;   means for comparing a node address in a destination node frame in a local area network message received from said first local area network with said table of addresses, and if said node address is associated with a bridge address, then enveloping said local area network message received from said first local area network in a backbone message data frame, said backbone message having a bridge destination frame containing said bridge address, and transmitting said backbone message to said backbone network, and if said node address is not associated with a bridge address, then enveloping said local area network message received from said first local area network in a backbone message data frame, said backbone message having a bridge destination frame containing a multicast bridge address, and transmitting said backbone message to said backbone network.   
     
     
       14. A bridge system for connecting networks, comprising a plurality of local area networks, each local area network comprising a plurality of nodes and each node having a unique node address, each network connected to a bridge and each bridge having a unique bridge address, each bridge connected to a backbone network, and wherein each bridge comprises: means for transmitting and receiving a local area network message to and from a first local area network;   means for transmitting and receiving a backbone network message to and from said backbone network;   a storage means for storing a table of addresses associating with node address with its respective bridge address;   means for comparing a node address in a destination node frame in a local area network message received from said first local area network with said table of addresses, and if said node address is associated with a bridge address of this particular bridge, then ignoring said local area network message, and if said node address is associated with a bridge address other than the bridge address associated with this particular bridge, then enveloping said local area network message received from said first local area network in a backbone message data frame, said backbone message having a bridge destination frame containing said bridge address, and transmitting said backbone message to said backbone network, and if said node address is not associated with a bridge address, then enveloping said local area network message received from said first local area network in a backbone message data frame, said backbone message having a bridge destination frame containing a multicast bridge address, and transmitting said backbone message to said backbone network.